It follows a stark warning from the Prime Minister that petrol prices must fall as the oil price tumbles or companies could end up facing a competition investigation.

The news also comes after the AA October Fuel Report revealed that Northern Ireland motorists are paying more for fuel than anywhere else in the UK.

Indeed, the latest figures show that drivers here – who are being billed, on average, 107.9p per litre of unleaded and 119.1p for diesel – are forking out 1.5p a litre more than motorists across the water.

Speaking to the Belfast Telegraph last night, Mr Dodds, MP, said there was no excuse for the shocking discrepancy.

“Northern Ireland motorists and hard-pressed households are also entitled to the same price reductions and benefits as other parts of the UK and there seems to be no justifiable reason for this differential in pricing,” he said.

“I have already raised this issue in the House of Commons and it certainly struck a chord with my fellow MPs. The pressure will go on and the criticism will go on until these retailers bring Northern Ireland into line with the rest of the country.”

Addressing Parliament last Thursday, Mr Dodds called for the matter to be tackled.

“Can we have a debate on fuel pricing in this country?” he said.

“Although there has been a welcome reduction in the petrol and diesel prices charged at the pumps in recent days, many motorists and households remain concerned about the extra costs imposed through the heavy levies of duty on fuel.

“They are also concerned about the practice of many retailers of operating a differential pricing policy depending on geographical location, so that the same retailer can charge different prices to motorists depending on where they live.

“That is clearly unfair and discriminatory, particularly to my constituents in Northern Ireland. I would therefore be grateful if we could have a debate to discuss those issues.”

On the same day, Gordon Brown accused retailers of charging too much and threatened them with an inquiry under competition laws if they refuse to pass on lower oil prices to motorists.

Oil has fallen to a 15-month low of less than $67 a barrel – its lowest level since May – but petrol prices have failed to come down accordingly.

And, as the Belfast Telegraph has repeatedly revealed, the extent of the price variations means that some garages are still charging up to £1.20 a litre in parts of the country.

Mr Brown told a press conference in Brussels at the close of a European Union summit that “some oil companies are not passing on reductions in oil prices”.

He added: “I think the public know that when oil prices go up it is reflected very quickly in the pump price.

“What we want to know is that when oil prices come down, it is reflected in pump prices. I think you will see over the next few days people giving this a great deal of attention.”

Firms including Asda last week dropped their prices to below £1 a litre. But with only seven filling stations in Northern Ireland, many motorists are likely to be unable to avail of the cheaper fuel on offer.

Sainsbury’s met Asda’s tariffs by cutting petrol to 99.9p a litre and diesel to 110.9p at some of their seven forecourts here.

Tesco, the UK’s biggest supermarket chain, reduced unleaded to 99.9p and diesel to a low of 111.9p at some sites – but not at any of its 12 Northern Ireland forecourts.

The AA said that drivers were benefiting directly from the falling oil prices. It said average petrol prices have fallen by 6.5p a litre over the past month.

“Its report, a mid-month snapshot of fuel prices across the UK, does not reflect the supermarket price war in which prices dropped below £1 a litre.

Average petrol prices between mid-September and mid-October fell from 112.9p a litre to 106.4p. Diesel went down from 124.26p to 117.68p.

But motorists in Northern Ireland are still paying over the odds compared to their British counterparts.

AA Public Affairs spokesman Luke Bosdet said the situation was “very difficult to stomach”.

He added: “It seems almost unbelievable that a stretch of water separates prices which are 2p higher than the rest of the UK.”